Central California Ozone Study (CCOS) - Desert Research Institute

CCOS Field Operations Plan Version 2: 5/31/00
4.5 PERFORMANCE AUDIT PROCEDURES
4.5.1 Radar Profilers
Two sets of performance audit procedures will be used that are specific to given sites. If
the site is equipped with a collocated sodar, the profiling system will be audited by first
establishing the on-site sodar as an audit device and then using the sodar data collected to audit
the radar profiler data. Sites with a radar profiler only will be audited using a rawinsonde.
The new EPA guidance for QA on radar profilers defines a series of system checks
inherent to the profiler electronics. Unlike the sodar where instrumentation exists for simulation
of winds by introduction of “Doppler shifted frequencies” no such instrumentation exists for the
profiler or RASS systems. Thus, to audit the data gathered by these profilers, the data are
compared to measurements from multiple rawinsonde balloon launches. At least three launches
are performed over the course of a day to collect data under a variety of meteorological
conditions. The collected meteorological data are reduced into components along the radar wind
profiler axes and the speeds compared with the radar data. This method is consistent with the
newest EPA guidance (EPA 2000). Audit criteria for RWP and an overview of the procedures
are presented in Table 4.5-1.
As a final part of the audit of the radar profilers, data from several days prior to the audit
are reviewed for internal consistency. This type of review checks indicated flags for data
reliability or quality codes for consistency, individual component intensity values to identify
potential reflections, and the vertical profiles of the components and resultant values for internal
consistency both in space and time. This is a subjective review and has proved useful in past
audits as a “second set of eyes” reviewing the data.
4.5.2 RASS
Audits of the RASS measurements are performed using at least three launches of
rawinsondes over the course of the day. The sondes measure pressure, temperature and relative
humidity and are used to calculate the virtual temperature profiles (Tv) for comparison to the
RASS-derived Tv values. The data collected from each launch are averaged to match the
averaging intervals of the RASS. Audit criteria used for evaluating results are shown in Table
4.5-1. Experience gained in the LMOS, IMS-95 and NARSTO-Northeast and SCOS97-
NARSTO studies showed this criterion is readily achievable. However, differences outside of
this criterion do not mean the RASS system has failed. It indicates that the data need further
analysis to determine the reasons for the differences and potential corrective action.
As in the wind profiles, data from several days prior to the audit will be reviewed. The
review will focus on the internal consistency of the data in both space and time and look for the
reasonableness of the Tv profiles.
Chapter 4: QUALITY ASSURANCE 4-15